payment plans?

So, now and then (a handful of times a year schedule permitting) I like to make and sell premade partials/heads. Typically I do not accept payment plans because I do not want to deal with the hassle of them. However, I'm considering it because I do not want to alienate people from bidding on suits. Although I may still require full payment on things that are like 3-4 hundred ish.
My question is how do you guys handle payment plans (those who accept them?) My fear is getting my time wasted by someone who is not -totally- invested, isn't financially in a position to make a big purchase (but tries anyway) and I end up getting my time wasted. I don't want to have to chase people for payments, that's why I usually just say payment in full up front. STILL, I wanted to see how other people do it, and maybe I'm just making taking payments a bigger deal then it needs to be.

My big things are -- how long do you guys give? A week between payments? A month? Are all payments non-refundable? I'm concerned of scenarios like...I get two payments out of three or four and then the person tries to back out (and maybe get their money back). I feel like saying if I do accept payment plans then all payments are non-refundable in order to prevent (or make less likely) a situation like that from happening. I also don't want to have to wait three four months for money either. I guess I'm looking for examples of situations from people that are fair to buyer/seller that makes payment plans an option I can possibly offer in the future. :)

Thanks!